The present invention relates to paper machines.
In particular, the present invention relates to a paper machine suitable for manufacturing tissue paper.
The paper machine includes a forming section where a pair of endless fabrics cooperate to provide an ascending twin-wire former as well as a single-wire former in advance of the twin-wire former, with a headbox supplying pulp suspension onto the single-wire former, suitable forming rolls cooperating with the endless fabrics and providing a web-draining region therewith.
As is well known, tissue paper is commonly manufactured by forming a web on a fairly short wire section resembling a normal planar wire where the headbox supplies the stock onto a breast roll which is often open or provided with an interior vacuum. The web travels beyond the breast roll supported by the wire past conventional dewatering elements such as table roll deflectors, foil laths, suction boxes and a suction roll, each of which removes water from the forming web. At the end of wire section the partly dried web is transferred onto a so-called pick-up felt, and while supported thereby it passes, while being subjected to further drying, to the press and drying sections of the machine. In some machines the planar wire part has been entirely omitted. Instead, web formation takes place, in this case, in its entirety on the suction breast roll which is wire-coated and from which the web is directly transferred to the pick-up felt. The above conventional constructions have a serious drawback, among others, in that the upper speed limit of the paper machine will be on the order of 1500 m/min., because the draining pressure tends to become excessively high with the result that the web will undesirably adhere to the wire.
Several twin-wire formers intended for manufacturing tissue paper also are known in the art. Most of these twin-wire formers are so-called full throat formers, but this type of construction has generally had the drawback that as a result of the full-throat forming there is a poor formation of the web with the web also adhering undesirably to the wire as a result of high draining pressure. These drawbacks result in splitting of the paper. In addition, there is the further drawback of poor retention of fibers and filler substances.
With respect to prior patent literature which may be pertinent, reference may be made, by way of example, to Canadian Pat. No. 968,601, which relates to the same general field as the present invention and which discloses a certain type of pick-up press. Reference also may be made to U.S. Pat. Nos. 3,378,435 and 3,537,954, the first of these patents providing the machine commonly known as the Crescent former. Reference may also be made to the presently pending U.S. patent application Ser. No. 730,444 filed May 20, 1968. Another commonly known former construction is illustrated in British Pat. No. 1,244,040 in which the so-called Papriformer of AB Karlstads Mekaniska Verkstad is shown.
With respect to the construction of the paper machine of the present invention, this machine of the present invention is a further development of the twin-wire former disclosed in U.S. Pat. No. 3,846,232 and in the associated continuation-in-part application Ser. No. 493,704 filed July 31, 1974, now U.S. Pat. No. 3,997,390. With respect to these structures, reference is particularly directed to the single-wire initial part of the former, with respect to the possibility of regulating the various process variables in a manner to which the practical paper maker is already accustomed in connection with Fourdrinier paper machines. In this connection, most important among these process variables are the discharge velocity of the stock jet with reference to the wire, the contact angle of the stock jet with the wire, and the rate at which water is drained from the suspension conducted onto the wire.